1. Field of the Invention
The present invention relates to a semiconductor device and a method of testing the semiconductor device.
2. Description of the Background Art
Power devices functioning as power semiconductor elements have been applied as contactless switches for controlling high-capacity power in inverter circuits of household electric appliances such as air conditioners, refrigerators and washers for which energy saving has been promoted. These power devices have also been applied for motor control of electric trains such as the bullet trains and subway trains. In recent years, these power devices have been applied in a wider range of fields in consideration especially of the Earth's environment, and have been used as those for controlling inverters and converters of hybrid cars that use electricity and engines in combination, and as converters for photovoltaic power generation and wind power generation. A semiconductor chip including these power devices is disclosed for example in Japanese Patent Application Laid-Open No. 2005-322781.
A technique to reduce the thickness of a semiconductor chip is mainly employed to enhance the electric characteristics of the semiconductor chip. However, thickness reduction of a semiconductor chip results in variations of stress applied in the plane of the semiconductor chip, and these variations make the nonuniformity of the electric characteristics more series in the plane. The serious nonuniformity of the electric characteristics causes a large current to flow partially in the semiconductor chip. So, heat with a high heating value is generated in the part where the large current flows, resulting in a fear of shortened lifetime of a semiconductor device. Also, it has been impossible to determine if quality degradation generated during a high-temperature storage test or during a power cycle test is due to stress, or failure during manufacture of chips.